Sprague-Dawley rats are conditioned and maintained throughout pregnancy and lactation on one of the following protein-fat test diets (8% casein - 10% corn oil; 19.5% casein - 10% corn oil; 31% casein - 10% corn oil). The female neonates are maintained on the respective diets throughout development. Standard DMBA mammary tumors are induced. Prior to and after DMBA treatment biogenic amine (NE, Epi, DA and 5-HT) activity in four hypothalamic nuclei and serum prolactin, estradiol and progesterone activity are determined. Tumor induction, growth and morphologic characteristics are related to diet. The data is being evaluated to establish a molecular and physiologic mechanism for the relationship between protein diets and mammary tumor characteristics.